1. Technical Field
The present invention relates to an image reading device including an image forming optical device that forms an erect equal-magnification image by forming an image of reflected light from an object to be read.
2. Related Art
In the related art, a contact image sensor module (hereinafter, simply referred to as “CIS module”) is used as an image reading device in image scanners, facsimiles, copy machines, financial terminal devices, and the like. The CIS module includes an illumination unit that illuminates an object to be read, an image forming optical device that forms an erect equal-magnification image of the object to be read, and a sensor that reads the erect equal-magnification image formed by the image forming optical device. In the CIS module, reflected light from the object illuminated by the illumination unit is condensed by the image forming optical device, and thus the erect equal-magnification image is formed on the sensor. For example, Japanese Patent No. 4145271 (paragraphs 0020 to 0022, FIG. 1, and the like) discloses an image reading device which includes an illumination unit disposed close to an image forming optical device along the longitudinal direction in which a rod-shaped light guide body formed of a transparent member such as an acryl resin is accommodated in a case. In addition, the light guide body includes a reflecting surface at the bottom in which a reflection structure is formed, right and left side surfaces that are formed as an elliptical curved surface, a parabolic curved surface, or a composite curved surface thereof, and a flat light emitting surface that is disposed so as to face the reflecting surface in a cross-sectional shape perpendicular to the longitudinal direction. Therefore, light of a light source, which is incident from an end surface of the light guide body and is scattered on the reflecting surface, is reflected by the right and left side surfaces of the light guide body, and is then emitted toward an object to be read from the light emitting surface.
Incidentally, in order to form a clear erect equal-magnification image on a sensor using the image forming optical device, a portion where the object to be read and an optical axis of a lens array included in the image forming optical device intersect needs to be sufficiently illuminated in the form of a band using an illumination unit. Therefore, a technique to illuminate the object to be read with high efficiency is required.